Analysis on Ultimate Load Capacity of Cylinder With Local Discontinuity Under High Temperature Gradient

Abstract

A severe accident management concept, known as ‘in-vessel retention (IVR)’, is widely used in advanced pressurized water reactor, such as AP600, AP1000, and so on. The severe accident management strategy is to flood the reactor cavity, submerging the reactor pressure vessel (RPV). In such condition, the temperature on the inside of RPV may exceed the melting point (about 1327 °C) of RPV material, and results in the localized wall thinning. On the outside, the temperature is remained at about 127 °C, by assuming the flow regime is kept to be nucleate boiling. So it will form a high temperature gradient on the wall, and caused high thermal stress. It will bring about the local discontinuity on the PRV wall because of the wall molten under the elevated temperature. A cylinder model is established to simulate the local discontinuity. The model is composed of the cylinder with the same external radius, but different wall thickness in the local discontinuity zone. Two elastic perfectly plastic models are used to analyze the stress and strain distributions on the wall and ultimate load capacity, based on the hot tensile curves and isochronous stress-strain curves at 100 hour with the change of temperature. The effect of local discontinuity is discussed, under the case of high temperature gradient and internal pressure. The results show that the Mises stress on the whole wall-thickness in the region of local discontinuity will achieve yield stress, under the high thermal stress. Appling internal pressure, the stress decreases in the zone of local discontinuity. The weakest link takes place in the thin segment of the cylinder model, and the ultimate pressure is obtained.